1. Field of Invention
The present invention relates to a timepiece with a wireless communication function for receiving radio frequency signals.
2. Description of Related Art
Timepieces that have a wireless communication function are known from the literature. One use for such wireless communication functions is receiving signals from positioning information satellites such as GPS (Global Positioning System) satellites to detect the current position.
When a wireless communication function is rendered in a wristwatch as such a timepiece with a wireless communication function, an antenna with sufficient reception performance must be rendered in a confined space.
Wristwatches that can function as a reception terminal in a satellite communication system, and wristwatches with a function for sending and receiving RF transmission signals, are taught in Japanese Unexamined Patent Appl. Pub. JP-A-2000-59241, Japanese Unexamined Patent Appl. Pub. JPA-2001-27680, and Japanese Unexamined Patent Appl. Pub. JP-A-H10-160872.
In the wristwatch taught in JP-A-2000-59241, a C-shaped loop antenna with a dielectric substrate is disposed around the display unit, and the metal case member of the wristwatch is used as a ground plate.
In the wristwatch taught in JP-A-2001-27680, a GPS antenna is disposed beside the display unit of the wristwatch. The GPS antenna is affixed to the metal wristwatch case with double-sided tape.
In the wristwatch taught in JP-A-H10-160872, the antenna and communication circuit are together rendered in a plastic bezel, and a communication mechanism can be easily added to the wristwatch by simply installing the bezel. The antenna is covered by the bezel and cannot be seen from the outside.
In addition to practical functions such as displaying the time and communication functions, a high quality appearance is also desirable in a timepiece. This is particularly true for analog wristwatches.
Metal materials with a precision finish are commonly used for the case, dial, and other external parts of such timepieces. Functional elements such as communication antennas in particular must be covered or rendered internally so that they do not detract from the external appearance.
With the timepieces taught in JP-A-2000-59241 and JPA-2001-27680, the communications antenna is large and exposed beside the display unit, and cannot be used if a quality appearance is also a consideration.
The configuration taught in JP-A-H10-160872 largely obviates appearance-related problems, but cannot assure sufficient antenna performance. More specifically, the communications antenna is not exposed but a ground plate cannot be assured.
In addition, while a metal case and dial are desirable for appearance considerations, their conductivity also makes them function as an electromagnetic shield blocking RF signals from the inside. As a result, when the antenna is disposed inside a metal case and dial, sufficient antenna performance cannot be achieved.